On Manures. 215 



ge table matter in the soil, so as to become the food of growing 

 plants ; and is of use as an exciting manure, rendering the 

 soil more prolific, by giving a new stimulus to enriching ma- 

 nures. It also acts, by improving the mechanical arrangement 

 of the soil. It tends to bind and consolidate a soil that is too 

 light and loose, and attracts moisture to it from the atmo- 

 sphere ; and it opens the pores of a clay or adhesive soil, and 

 reduces its tenacity. Wherever vegetable matter abounds, 

 either in the state of herbage or sward, or in a more decayed 

 state in the soil, lime, if judiciously applied, in a dry and 

 powdery form, will bring it into action, to the powerful sup- 

 port of growing plants. But where little vegetable matter 

 prevails, or where it has been already much reduced by pre- 

 vious liming, farther applications of that substance can do no 

 good, but may be injurious. Lime, whether applied when hot 

 and powdery, or when it has again absorbed carbonic acid, and 

 become more damp and solid, has great lasting effects on the 

 mechanical arrangement of the soil. The action of lime, in 

 reducing vegetable matter to operate as food for plants, is 

 speedy and powerful ; whereas, in opening the pores of clay, 

 it acts slower, but more permanently. One of its principal 

 advantages is, that by its agency, iron pyrites, a combination 

 of iron and sulphur, very common in some soils, and very 

 hostile to vegetation, is decomposed. 



4. The various sorts of Limestone. Sometimes limestone is 

 almost perfectly pure, as is the case with marble, which fre- 

 quently contains scarcely any other substance than carbonate 

 of lime. Several sorts of limestone however, have mixtures 

 of clay and sand, in various proportions, by which the efficacy 

 of the manure, in proportion to the quantity of these sub- 

 stances, is considerably diminished. It is necessary, there- 

 fore, to analyze limestone, to ascertain the proportion of pure 

 lime, before it becomes advisable to use so expensive an article 

 in great quantities, more especially if it must be conveyed from 

 a distance ( il3 ). Bituminous limestone makes good manure. 

 But the magnesian is the species which requires the greatest 

 attention, for though it usually contains only from 20.3 to 

 23.5 of magnesia, yet, Mr Tennant found, that the proportion 

 of that substance, sometimes reached even 40 per cent. From 

 the peculiar qualities of that lime however, it would in gene- 

 ral be injurious, to apply more than from 25 to 30 bushels 

 per statute acre, though, in very rich soils, that quantity may 

 be increased, and still more with peat, on which its application 

 in abundance, would have a most powerful effect in producing 

 futility ('). 



